Antenna array communication using spreading codes

ABSTRACT

A first reference signal and a first data signal are transmitted from a first antenna of a base station and a second reference signal and a second data signal are transmitted from a second antenna of the base station. The first and second antennas are difference antennas. The first and second reference signals having different codes and the first and second data signals having different codes. The received first and second reference signals are combined using an adaptive algorithm producing adaptive algorithm weights. Data from the first and second data signals is recovered by combining the first and second data signal in response to adaptive algorithm weights.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/068,718, filed Feb. 6, 2002, which issued onJan. 3, 2006 as U.S. Pat. No. 6,983,008; which is a continuation of U.S.patent application Ser. No. 10/068,659, filed Feb. 6, 2002, which issuedon Jun. 3, 2003 as U.S. Pat. No. 6,574,265, which is a continuation ofU.S. patent application Ser. No. 09/602,963, filed Jun. 23, 2000, whichissued on Apr. 16, 2002 as U.S. Pat. No. 6,373,877; which is acontinuation of U.S. patent application Ser. No. 09/394,452 filed Sep.10, 1999, which issued on Sep. 5, 2000 as U.S. Pat. No. 6,115,406.

FIELD OF THE INVENTION

The present invention relates generally to signal transmission andreception in a wireless code division multiple access (CDMA)communication system. More specifically, the invention relates to asystem and method of transmission using an antenna array to improvesignal reception in a wireless CDMA communication system.

BACKGROUND

A prior art CDMA communication system is shown in FIG. 1. Thecommunication system has a plurality of base stations 20-32. Each basestation 20 communicates using spread spectrum CDMA with user equipment(UEs) 34-38 within its operating area. Communications from the basestation 20 to each UE 34-38 are referred to as downlink communicationsand communications from each UE 34-38 to the base station 20 arereferred to as uplink communications.

Shown in FIG. 2 is a simplified CDMA transmitter and receiver. A datasignal having a given bandwidth is mixed by a mixer 40 with a pseudorandom chip code sequence producing a digital spread spectrum signal fortransmission by an antenna 42. Upon reception at an antenna 44, the datais reproduced after correlation at a mixer 46 with the same pseudorandom chip code sequence used to transmit the data. By using differentpseudo random chip code sequences, many data signals use the samechannel bandwidth. In particular, a base station 20 will communicatesignals to multiple UEs 34-38 over the same bandwidth.

For timing synchronization with a receiver, an unmodulated pilot signalis used. The pilot signal allows respective receivers to synchronizewith a given transmitter allowing despreading of a data signal at thereceiver. In a typical CDMA system, each base station 20 sends a uniquepilot signal received by all UEs 34-38 within communicating range tosynchronize forward link transmissions. Conversely, in some CDMAsystems, for example in the B-CDMA™ air interface, each UE 34-38transmits a unique assigned pilot signal to synchronize reverse linktransmissions.

When a UE 34-36 or a base station 20-32 is receiving a specific signal,all the other signals within the same bandwidth are noise-like inrelation to the specific signal. Increasing the power level of onesignal degrades all other signals within the same bandwidth. However,reducing the power level too far results in an undesirable receivedsignal quality. One indicator used to measure the received signalquality is the signal to noise ratio (SNR). At the receiver, themagnitude of the desired received signal is compared to the magnitude ofthe received noise. The data within a transmitted signal received with ahigh SNR is readily recovered at the receiver. A low SNR leads to lossof data.

To maintain a desired signal to noise ratio at the minimum transmissionpower level, most CDMA systems utilize some form of adaptive powercontrol. By minimizing the transmission power, the noise between signalswithin the same bandwidth is reduced. Accordingly, the maximum number ofsignals received at the desired signal to noise ratio within the samebandwidth is increased.

Although adaptive power control reduces interference between signals inthe same bandwidth, interference still exists limiting the capacity ofthe system. One technique for increasing the number of signals using thesame radio frequency (RF) spectrum is to use sectorization. Insectorization, a base station uses directional antennas to divide thebase station's operating area into a number of sectors. As a result,interference between signals in differing sectors is reduced. However,signals within the same bandwidth within the same sector interfere withone another. Additionally, sectorized base stations commonly assigndifferent frequencies to adjoining sectors decreasing the spectralefficiency for a given frequency bandwidth. Accordingly, there exists aneed for a system which further improves the signal quality of receivedsignals without increasing transmitter power levels.

SUMMARY OF THE INVENTION

A first reference signal and a first data signal are transmitted from afirst antenna of a base station and a second reference signal and asecond data signal are transmitted from a second antenna of the basestation. The first and second antennas are difference antennas. Thefirst and second reference signals having different codes and the firstand second data signals having different codes. The received first andsecond reference signals are combined using an adaptive algorithmproducing adaptive algorithm weights. Data from the first and seconddata signals is recovered by combining the first and second data signalin response to adaptive algorithm weights.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art wireless spread spectrum CDMA communicationsystem.

FIG. 2 is a prior art spread spectrum CDMA transmitter and receiver.

FIG. 3 is the transmitter of the invention.

FIG. 4 is the transmitter of the invention transmitting multiple datasignals.

FIG. 5 is the pilot signal receiving circuit of the invention.

FIG. 6 is the data signal receiving circuit of the invention.

FIG. 7 is an embodiment of the pilot signal receiving circuit.

FIG. 8 is a least mean squarred weighting circuit.

FIG. 9 is the data signal receiving circuit used with the pilot signalreceiving circuit of FIG. 7.

FIG. 10 is an embodiment of the pilot signal receiving circuit where theoutput of each RAKE is weighted.

FIG. 11 is the data signal receiving circuit used with the pilot signalreceiving circuit of FIG. 10.

FIG. 12 is an embodiment of the pilot signal receiving circuit where theantennas of the transmitting array are closely spaced.

FIG. 13 is the data signal receiving circuit used with the pilot signalreceiving circuit of FIG. 12.

FIG. 14 is an illustration of beam steering in a CDMA communicationsystem.

FIG. 15 is a beam steering transmitter.

FIG. 16 is a beam steering transmitter transmitting multiple datasignals.

FIG. 17 is the data receiving circuit used with the transmitter of FIG.14.

FIG. 18 is a pilot signal receiving circuit used when uplink anddownlink signals use the same frequency.

FIG. 19 is a transmitting circuit used with the pilot signal receivingcircuit of FIG. 18.

FIG. 20 is a data signal receiving circuit used with the pilot signalreceiving circuit of FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments will be described with reference to thedrawing figures where like numerals represent like elements throughout.FIG. 3 is a transmitter of the invention. The transmitter has an arrayof antennas 48-52, preferably 3 or 4 antennas. For use in distinguishingeach antenna 48-52, a different signal is associated with each antenna56-60. The preferred signal to associate with each antenna is a pilotsignal as shown in FIG. 3. Each spread pilot signal is generated by apilot signal generator 56-60 using a different pseudo random chip codesequence and is combined by combiners 62-66 with the respective spreaddata signal. Each spread data signal is generated using data signalgenerator 54 by mixing at mixers 378-382 the generated data signal witha different pseudo random chip code sequence per antenna 48-52,D₁-D_(N). The combined signals are modulated to a desired carrierfrequency and radiated through the antennas 48-52 of the array.

By using an antenna array, the transmitter utilizes spacial diversity.If spaced far enough apart, the signals radiated by each antenna 48-52will experience different multipath distortion while traveling to agiven receiver. Since each signal sent by an antenna 48-52 will followmultiple paths to a given receiver, each received signal will have manymultipath components. These components create a virtual communicationchannel between each antenna 48-52 of the transmitter and the receiver.Effectively, when signals transmitted by one antenna 48-52 over avirtual channel to a given receiver are fading, signals from the otherantennas 48-52 are used to maintain a high received SNR. This effect isachieved by the adaptive combining of the transmitted signals at thereceiver.

FIG. 4 shows the transmitter as used in a base station 20 to sendmultiple data signals. Each spread data signal is generated by mixing atmixers 360-376 a corresponding data signal from generators 74-78 withdiffering pseudo random chip code sequences D₁₁-D_(NM). Accordingly,each data signal is spread using a different pseudo random chip codesequence per antenna 48-52, totaling N×M code sequences. N is the numberof antennas and M is the number of data signals. Subsequently, eachspread data signal is combined with the spread pilot signal associatedwith the antenna 48-52. The combined signals are modulated and radiatedby the antennas 48-52 of the array.

The pilot signal receiving circuit is shown in FIG. 5. Each of thetransmitted pilot signals is received by the antenna 80. For each pilotsignal, a despreading device, such as a RAKE 82-86 as shown in the FIG.5 or a vector correlator, is used to despread each pilot signal using areplica of the corresponding pilot signal's pseudo random chip codesequence. The despreading device also compensates for multipath in thecommunication channel. Each of the recovered pilot signals is weightedby a weighting device 88-92. Weight refers to both magnitude and phaseof the signal. Although the weighting is shown as being coupled to aRAKE, the weighting device preferably also weights each finger of theRAKE. After weighting, all of the weighted recovered pilot signals arecombined in a combiner 94. Using an error signal generator 98, anestimate of the pilot signal provided by the weighted combination isused to create an error signal. Based on the error signal, the weightsof each weighting device 88-92 are adjusted to minimize the error signalusing an adaptive algorithm, such as least mean squared (LMS) orrecursive least squares (RLS). As a result, the signal quality of thecombined signal is maximized.

FIG. 6 depicts a data signal receiving circuit using the weightsdetermined by the pilot signal recovery circuit. The transmitted datasignal is recovered by the antenna 80. For each antenna 48-52 of thetransmitting array, the weights from a corresponding despreading device,shown as a RAKE 82-86, are used to filter the data signal using areplica of the data signal's spreading code used for the correspondingtransmitting antenna. Using the determined weights for each antenna'spilot signal, each weighting device 106-110 weights the RAKE's despreadsignal with the weight associated with the corresponding pilot. Forinstance, the weighting device 88 corresponds to the transmittingantenna 48 for pilot signal 1. The weight determined by the pilot RAKE82 for pilot signal 1 is also applied at the weighting device 106 ofFIG. 6. Additionally, if the weights of the RAKE's fingers were adjustedfor the corresponding pilots signal's RAKE 82-86, the same weights willbe applied to the fingers of the data signal's RAKE 100-104. Afterweighting, the weighted signals are combined by the combiner 112 torecover the original data signal.

By using the same weights for the data signal as used with eachantenna's pilot signal, each RAKE 82-86 compensates for the channeldistortion experienced by each antenna's signals. As a result, the datasignal receiving circuit optimizes the data signals reception over eachvirtual channel. By optimally combining each virtual channel's optimizedsignal, the received data signal's signal quality is increased.

FIG. 7 shows an embodiment of the pilot signal recovery circuit. Each ofthe transmitted pilots are recovered by the receiver's antenna 80. Todespread each of the pilots, each RAKE 82-86 utilizes a replica of thecorresponding pilot's pseudo random chip code sequence, P₁-P_(N).Delayed versions of each pilot signal are produced by delay devices114-124. Each delayed version is mixed by a mixer 126-142 with thereceived signal. The mixed signals pass through sum and dump circuits424-440 and are weighted using mixers 144-160 by an amount determined bythe weight adjustment device 170. The weighted multipath components foreach pilot are combined by a combiner 162-164. Each pilot's combinedoutput is combined by a combiner 94. Since a pilot signal has no data,the combined pilot signal should have a value of 1+j0. The combinedpilot signal is compared to the ideal value, 1+j0, at a subtractor 168.Based on the deviation of the combined pilot signal from the ideal, theweight of the weighting devices 144-160 are adjusted using an adaptivealgorithm by the weight adjustment device 170.

A LMS algorithm used for generating a weight is shown in FIG. 8. Theoutput of the subtractor 168 is multiplied using a mixer 172 with thecorresponding despread delayed version of the pilot. The multipliedresult is amplified by an amplifier 174 and integrated by an integrator176. The integrated result is used to weight, W_(1M), the RAKE finger.

The data receiving circuit used with the embodiment of FIG. 7 is showfor a base station receiver in FIG. 9. The received signal is sent to aset of RAKEs 100-104 respectively associated with each antenna 48-52 ofthe array. Each RAKE 100-104, produces delayed versions of the receivedsignal using delay devices 178-188. The delayed versions are weightedusing mixers 190-206 based on the weights determined for thecorresponding antenna's pilot signal. The weighted data signals for agiven RAKE 100-104 are combined by a combiner 208-212. One combiner208-212 is associated with each of the N transmitting antennas 48-52.Each combined signal is despread M times by mixing at a mixer 214-230the combined signal with a replica of the spreading codes used forproducing the M spread data signals at the transmitter, D₁₁-D_(NM). Eachdespread data signal passes through a sum and dump circuit 232-248. Foreach data signal, the results of the corresponding sum and dump circuitsare combined by a combiner 250-254 to recover each data signal.

Another pilot signal receiving circuit is shown in FIG. 10. Thedespreading circuits 82-86 of this receiving circuit are the same asFIG. 7. The output of each RAKE 82-86 is weighted using a mixer 256-260prior to combining the despread pilot signals. After combining, thecombined pilot signal is compared to the ideal value and the result ofthe comparison is used to adjust the weight of each RAKE's output usingan adaptive algorithm. To adjust the weights within each RAKE 82-86, theoutput of each RAKE 82-86 is compared to the ideal value using asubtractor 262-266. Based on the result of the comparison, the weight ofeach weighting device 144-160 is determined by the weight adjustmentdevices 268-272.

The data signal receiving circuit used with the embodiment of FIG. 10 isshown in FIG. 11. This circuit is similar to the data signal receivingcircuit of FIG. 9 with the addition of mixers 274-290 for weighting theoutput of each sum and dump circuit 232-248. The output of each sum anddump circuit 232-248 is weighted by the same amount as the correspondingpilot's RAKE 82-86 was weighted. Alternatively, the output of eachRAKE's combiner 208-212 may be weighted prior to mixing by the mixers214-230 by the amount of the corresponding pilot's RAKE 82-86 in lieu ofweighting after mixing.

If the spacing of the antennas 48-52 in the transmitting array is small,each antenna's signals will experience a similar multipath environment.In such cases, the pilot receiving circuit of FIG. 12 may be utilized.The weights for a selected one of the pilot signals are determined inthe same manner as in FIG. 10. However, since each pilot travels throughthe same virtual channel, to simplify the circuit, the same weights areused for despreading the other pilot signals. Delay devices 292-294produce delayed versions of the received signal. Each delayed version isweighted by a mixer 296-300 by the same weight as the correspondingdelayed version of the selected pilot signal was weighted. The outputsof the weighting devices are combined by a combiner 302. The combinedsignal is despread using replicas of the pilot signals' pseudo randomchip code sequences, P₂-P_(n), by the mixers 304-306. The output of eachpilot's mixer 304-306 is passed through a sum and dump circuit 308-310.In the same manner as FIG. 10, each despread pilot is weighted andcombined.

The data signal recovery circuit used with the embodiment of FIG. 12 isshown in FIG. 13. Delay devices 178-180 produce delayed versions of thereceived signal. Each delayed version is weighted using a mixer 190-194by the same weight as used by the pilot signals in FIG. 12. The outputsof the mixers are combined by a combiner 208. The output of the combiner208 is inputted to each data signal despreader of FIG. 13.

The invention also provides a technique for adaptive beam steering asillustrated in FIG. 14. Each signal sent by the antenna array willconstructively and destructively interfere in a pattern based on theweights provided each antenna 48-52 of the array. As a result, byselecting the appropriate weights, the beam 312-316 of the antenna arrayis directed in a desired direction.

FIG. 15 shows the beam steering transmitting circuit. The circuit issimilar to the circuit of FIG. 3 with the addition of weighting devices318-322. A target receiver will receive the pilot signals transmitted bythe array. Using the pilot signal receiving circuit of FIG. 5, thetarget receiver determines the weights for adjusting the output of eachpilot's RAKE. These weights are also sent to the transmitter, such as byusing a signaling channel. These weights are applied to the spread datasignal as shown in FIG. 15. For each antenna, the spread data signal isgiven a weight by the weighting devices 318-322 corresponding to theweight used for adjusting the antenna's pilot signal at the targetreceiver providing spatial gain. As a result, the radiated data signalwill be focused towards the target receiver. FIG. 16 shows the beamsteering transmitter as used in a base station sending multiple datasignals to differing target receivers. The weights received by thetarget receiver are applied to the corresponding data signals byweighting devices 324-340.

FIG. 17 depicts the data signal receiving circuit for the beam steeringtransmitter of FIGS. 15 and 16. Since the transmitted signal has alreadybeen weighted, the data signal receiving circuit does not require theweighting devices 106-110 of FIG. 6.

The advantage of the invention's beam steering are two-fold. Thetransmitted data signal is focused toward the target receiver improvingthe signal quality of the received signal. Conversely, the signal isfocused away from other receivers reducing interference to theirsignals. Due to both of these factors, the capacity of a system usingthe invention's beam steering is increased. Additionally, due to theadaptive algorithm used by the pilot signal receiving circuitry, theweights are dynamically adjusted. By adjusting the weights, a datasignal's beam will dynamically respond to a moving receiver ortransmitter as well as to changes in the multipath environment.

In a system using the same frequency for downlink and uplink signals,such as time division duplex (TDD), an alternate embodiment is used. Dueto reciprocity, downlink signals experience the same multipathenvironment as uplink signals send over the same frequency. To takeadvantage of reciprocity, the weights determined by the base station'sreceiver are applied to the base station's transmitter. In such asystem, the base station's receiving circuit of FIG. 18 is co-located,such as within a base station, with the transmitting circuit of FIG. 19.

In the receiving circuit of FIG. 18, each antenna 48-52 receives arespective pilot signal sent by the UE. Each pilot is filtered by a RAKE406-410 and weighted by a weighting device 412-416. The weighted andfiltered pilot signals are combined by a combiner 418. Using the errorsignal generator 420 and the weight adjustment device 422, the weightsassociated with the weighting devices 412-416 are adjusted using anadaptive algorithm.

The transmitting circuit of FIG. 19 has a data signal generator 342 togenerate a data signal. The data signal is spread using mixer 384. Thespread data signal is weighted by weighting devices 344-348 as weredetermined by the receiving circuit of FIG. 19 for each virtual channel.

The circuit of FIG. 20 is used as a data signal receiving circuit at thebase station. The transmitted data signal is received by the multipleantennas 48-52. A data RAKE 392-396 is coupled to each antenna 48-52 tofilter the data signal. The filtered data signals are weighted byweighting devices 398-402 by the weights determined for thecorresponding antenna's received pilot and are combined at combiner 404to recover the data signal. Since the transmitter circuit of FIG. 19transmits the data signal with the optimum weights, the recovered datasignal at the UE will have a higher signal quality than provided by theprior art.

1. A user equipment (UE) comprising: circuitry, operatively coupled toat least one antenna, configured to receive a spread spectrum signalcomprising a first pilot signal, a second pilot signal, and a datasignal; wherein the first pilot signal is associated with a firstantenna of a base station and the second pilot signal is associated witha second antenna of the base station and the first and second pilotsignal having a different chip sequence, wherein the received datasignal comprises two antenna specific chip sequences, each antennaspecific chip sequence being associated with the respective transmissionantenna; the circuitry further configured to process the first andsecond pilot signals to derive preferred weights for the data signal,wherein the first and second pilot signals have a different channel codethan the data signal; and circuitry configured to combine a data bitassociated with the first antenna with a corresponding data bitassociated with the second antenna using the preferred weights.
 2. TheUE of claim 1 further comprising: circuitry configured to weight thedata bit associated with the first antenna with the preferred weightsderived from the first pilot signal.
 3. The UE of claim 2, furthercomprising: circuitry configured to weight the data bit associated withthe second antenna with the preferred weights derived from the secondpilot signal.
 4. A method for use in a user equipment (UE), the methodcomprising: receiving a spread spectrum signal comprising a first pilotsignal, a second pilot signal, and a data signal; wherein the firstpilot signal is associated with a first antenna of a base station andthe second pilot signal is associated with a second antenna of the basestation and the first and second pilot signal having a different chipsequence, wherein the received data signal comprises two antennaspecific chip sequences, each antenna specific chip sequence beingassociated with the respective transmission antenna; processing thefirst and second pilot signals to derive preferred weights for the datasignal, wherein the first and second pilot signals have a differentchannel code than the data signal; and combining a data bit associatedwith the first antenna with a corresponding data bit associated with thesecond antenna using the preferred weights.
 5. The method of claim 4further comprising weighting the data bit associated with the firstantenna with the preferred weights derived from the first pilot signal.6. The method of claim 5, further comprising: weighting the data bitassociated with the second antenna with the preferred weights derivedfrom the second pilot signal.